Electrical control circuits of various types are commonly used in air conditioning and heat pump systems of various types, including compression and absorption refrigeration systems. Such systems typically include various sensors or switches as inputs and controls for various valves and pumps as outputs. In an absorption system the controlled functions are typically the solution pump, one or more coolant pumps or fans and a heat source associated with the generator such as a gas burner and ignition device.
The control system described in U.S. Pat. Nos. 3,527,060 and 3,527,061, issued Sept. 8, 1970 to Kruggel, includes a thermal time delay responsive to a thermostat which, after a delay, starts water coolant pumps, a diaphragm solution pump, a fan associated with an outside coil, and a gas burner. The delay, although inherent in the system, serves no useful purpose. When the thermostat senses no further demand, the gas burner is shut off and, after a delay attributable to the same thermal timer, the remaining power components are shut down. Several additional safety and control switches are also provided.
Such a timed system utilizes some of the refrigeration capacity or heating capacity of the system after gas burner shut off. The delay prior to unit activation serves no useful purpose, however, with all of the power components coming on at once.
Furthermore, since the gas flame is normally ventilated by the same fan that draws outside air over the outside coil, the gas supply and the fan come on at the same time. Since the absorption fluids may include a flammable component such as ammonia or ethyl tetrahydrofurfuryl ether, a flame started before activation of the fan to ventilate the apparatus has the potential of starting an uncontrolled fire.